KR102143101B1 - Method for preparing positive electrode active material for secondary battery, positive electrode active material prepared by the same and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides a lithium transition metal oxide; Forming a mixture by mixing the lithium transition metal oxide, a coating polymer, and a carbide; And forming a coating layer including a carbonized coating polymer and carbide on the surface of the particles of the lithium transition metal oxide by heat-treating the mixture. It provides a method for producing a cathode active material for a secondary battery comprising.

Description

Manufacturing method of positive electrode active material for secondary battery, positive electrode active material prepared in this way, and lithium secondary battery including the same {METHOD FOR PREPARING POSITIVE ELECTRODE ACTIVE MATERIAL FOR SECONDARY BATTERY, POSITIVE ELECTRODE ACTIVE MATERIAL PREPARED BY THE SAME AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a method of manufacturing a positive electrode active material for a secondary battery, a positive electrode active material thus prepared, and a lithium secondary battery including the same.

2. Description of the Related Art With the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries, which are small, lightweight, and relatively high-capacity is rapidly increasing. In particular, lithium secondary batteries are in the spotlight as driving power sources for portable devices due to their light weight and high energy density. Accordingly, research and development efforts to improve the performance of lithium secondary batteries have been actively conducted.

The lithium secondary battery is oxidized when lithium ions are inserted/detached from the positive electrode and the negative electrode while the organic electrolyte or the polymer electrolyte is charged between the positive electrode and the negative electrode made of an active material capable of intercalations and deintercalation of lithium ions. Electric energy is produced by the reduction reaction with.

Lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMnO ₂ or LiMn ₂ O ₄ etc.), lithium iron phosphate compound (LiFePO ₄ ), etc. are mainly used as positive active materials for lithium secondary batteries. do. In addition, as a method for improving low thermal stability while maintaining excellent reversible capacity of LiNiO ₂ , a method of substituting part of nickel (Ni) with cobalt (Co) or manganese (Mn) has been proposed. However, LiNi _{1 - α} Co _α O ₂ (α=0.1~0.3) in which a part of nickel is replaced with cobalt shows excellent charge/discharge characteristics and lifespan characteristics, but has low thermal stability. Meanwhile, a nickel manganese-based lithium composite metal oxide in which a part of nickel (Ni) is replaced with manganese (Mn) with excellent thermal stability, and a nickel cobalt-manganese-based lithium composite metal oxide substituted with manganese (Mn) and cobalt (Co) (hereinafter Simply referred to as'NCM-based lithium oxide') has the advantage of relatively excellent cycle characteristics and thermal stability.

Recently, the demand for high capacity and high energy density is gradually increasing, and an attempt is made to realize a target energy density by increasing the voltage by expanding the driving voltage range. Accordingly, there is a need to develop a high voltage withstand positive electrode active material having reliability and stability under a charging voltage condition of 4.35V or higher, which is a higher voltage than the existing 4.3V or lower.

In particular, in the high voltage state, there is a problem of a decrease in life characteristics and an increase in resistance due to an increase in side reactions with the electrolyte and the formation of a solid electrolyte interface (SEI) film on the surface of the positive electrode active material.

Korean Patent Publication No. 2012-0026466

An object of the present invention is to provide a positive electrode active material for a high-voltage secondary battery with improved resistance characteristics and life characteristics, suppressing side reactions with an electrolyte solution and formation of a solid electrolyte interface (SEI) film on the surface of a positive electrode active material under high voltage.

The present invention provides a lithium transition metal oxide; Forming a mixture by mixing the lithium transition metal oxide, a coating polymer, and a carbide; And forming a coating layer including a carbonized coating polymer and carbide on the surface of the particles of the lithium transition metal oxide by heat-treating the mixture. It provides a method for producing a cathode active material for a secondary battery comprising.

In addition, the present invention is a lithium transition metal oxide; And a coating layer formed on the particle surface of the lithium transition metal oxide, wherein the coating layer is formed in a film form, and the coating layer provides a cathode active material for a secondary battery comprising a carbonized coating polymer and carbide.

In addition, the present invention provides a positive electrode and a lithium secondary battery comprising the positive electrode active material.

According to the present invention, a positive electrode active material for a high voltage secondary battery with improved resistance characteristics and life characteristics can be prepared by suppressing side reactions with an electrolyte solution under high voltage and formation of a solid electrolyte interface (SEI) film on the surface of a positive electrode active material.

The positive electrode active material for a secondary battery according to the present invention can prevent mechanical damage of the positive electrode active material that occurs while repeating charging/discharging in a high voltage state. In addition, it is possible to uniformly coat the entire surface of the positive electrode active material particle, and reduce initial resistance and resistance increase rate by securing excellent electrical conductivity.

1 and 2 are scanning electron microscope (SEM, Scanning Electron Microscope) photographs of an enlarged observation of a positive electrode active material prepared according to Example 1 of the present invention.
3 and 4 are scanning electron microscope (SEM) photographs of an enlarged observation of a positive active material prepared according to Comparative Example 2.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention. At this time, terms or words used in the present specification and claims should not be construed as being limited to a conventional or dictionary meaning, and the inventor appropriately defines the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that it can be done.

The method for preparing a positive electrode active material for a secondary battery of the present invention comprises: preparing a lithium transition metal oxide; Forming a mixture by mixing the lithium transition metal oxide, a coating polymer, and a carbide; And forming a coating layer including a carbonized coating polymer and carbide on the surface of the particles of the lithium transition metal oxide by heat treatment of the mixture.

The present invention coats lithium transition metal oxide particles using a mixture of a coating polymer and carbide, thereby inhibiting side reactions with the electrolyte and the formation of a solid electrolyte interface (SEI) film on the surface of the positive electrode active material under high voltage, and resistance properties. And it is possible to improve the life characteristics. By using a soft material coating polymer, it is possible to prevent mechanical damage of the positive electrode active material that occurs while repeating charging/discharging in a high voltage state, and initial resistance due to securing excellent electrical conductivity by using a carbide with excellent electrical conductivity. And it is possible to reduce the resistance increase rate. In addition, the coating polymer may be carbonized through heat treatment during the coating process to secure additional electrical conductivity.

The method of manufacturing the positive electrode active material for a secondary battery of the present invention will be described in detail step by step below.

First, a lithium transition metal oxide is prepared.

The lithium transition metal oxide may be a lithium transition metal oxide, which is typically used as a positive electrode active material, more preferably any one or more transition metals selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn). Lithium transition metal oxides containing cations may be used. For example, layered compounds such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), or the formula Li _1+x1 Mn _2-x1 O ₄ (where x1 is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , lithium manganese oxide such as LiMnO ₂ , the formula LiNi _{1 - x2} M ¹ _x2 O ₂ (where M ¹ = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x2 = 0.01 ~ 0.3 ) Ni site-type lithium nickel oxide, the formula LiMn _2-x3 M ² _x3 O ₂ (where M ² = Co, Ni, Fe, Cr, Zn or Ta, x3 = 0.01 ~ 0.1) or Li ₂ Mn ₃ M ³ O ₈ (here, M ³ = Fe, Co, Ni, Cu, or Zn) lithium manganese complex oxide, LiNi _x4 Mn _{2 - x4} O ₄ (here, x4 = 0.01 ~ 1) Structure of lithium manganese composite oxide, lithium iron phosphate compound (LiFePO ₄ ), etc., but are not limited thereto, more preferably lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese It may be an oxide (LiMn ₂ O ₄ ), a lithium iron phosphate compound (LiFePO ₄ ), or the like.

Alternatively, as the positive electrode active material, a lithium transition metal composite oxide represented by Formula 1 may be included.

[Formula 1]

Li _p Ni _1-xy Co _x M ^a _y M ^b _z O ₂

In the above formula, M ^a is at least one element selected from the group consisting of Mn, Al and Zr, and M ^b is at least one selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo, W and Cr The above elements are 0.9≦p≦1.5, 0≦x≦0.5, 0≦y≦0.5, and 0≦z≦0.1. More preferably 0≦x+y≦0.7, most preferably 0<x+y≦0.4, and a high-Ni NCM-based positive electrode active material having a nickel (Ni) content of 60 mol% or more among the total transition metals Can be For example, the positive electrode active material is more preferably LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _{0 . 9} Co _{0 . 05} Mn _{0 . 05} O _{2 ,} or LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ It may be a High-Ni NCM-based lithium transition metal oxide such as.

Next, the lithium transition metal oxide, a coating polymer, and a carbide are mixed to form a mixture.

The coating polymer can be used as long as it can coat the particle surface of lithium transition metal oxide and does not degrade electrochemical performance. For example, polyvinylidene fluoride (PVDF), polyvinylpyrrolidone ( Polyvinylpyrrolidone), polyethylene, polystyrene, polyethylene terephthalate, polyvinyl chloride, polyvinylidene chloride, epoxy resin, amino resin, phenol resin, polyester resin may be at least one selected from the group consisting of, more preferably polyvinylidene At least one selected from the group consisting of fluoride (PVDF), polyvinylpyrrolidone, polyethylene terephthalate, and polyvinylidene chloride may be used.

By using the flexible material for coating polymer, it is possible to prevent mechanical damage to the positive electrode active material that occurs while repeating charging/discharging in a high voltage state. In addition, the formation of the coating layer through the conventional dry coating method of metal oxide was difficult to coat in an island form and uniformly in a film form, but the present invention coated with a mixture of the coating polymer and carbide. In this case, a uniform coating layer in the form of a film can be easily formed through temperature control during the coating process based on the melting point of the coating polymer, and the carbide mixed with the coating polymer is uniformly applied to the surface of the positive electrode active material particles. Can be distributed. In addition, the coating polymer may be carbonized through heat treatment during the coating process to secure additional electrical conductivity.

The coating polymer may be included in an amount of 0.001 to 10 parts by weight, more preferably 0.005 to 5 parts by weight, based on 100 parts by weight of the lithium transition metal oxide contained in the mixture. Since the coating polymer is mixed in an amount of 0.001 to 10 parts by weight relative to 100 parts by weight of lithium transition metal oxide, a coating layer can be uniformly formed on the entire surface of the positive electrode active material particles, and the coating layer formed as described above can be charged/discharged in a high voltage state. It is possible to prevent mechanical damage of the positive electrode active material that occurs while repeating.

The carbide (carbide) is a compound consisting of carbon and another element, for example, at least one selected from the group consisting of B ₄ C, Al ₄ C ₃ , TiC, TaC, WC, NbC, HfC, VC and ZrC It may be more, more preferably B ₄ C or Al ₄ C ₃ It may be.

The carbide (carbide) is covalently bonded with carbon and other elements, and has a relatively high melting point, so that it is not decomposed into CO ₂ or CO even during high temperature heat treatment in an oxidizing atmosphere during the coating process, and can remain as it is. It may be coated to be uniformly distributed on the surface of the positive electrode active material particles together with the solvent polymer. Through this, excellent electrical conductivity can be secured, and initial resistance and resistance increase rate can be reduced by securing excellent electrical conductivity.

The carbide (carbide) may be included in an amount of 0.001 to 10 parts by weight, more preferably 0.002 to 2 parts by weight based on 100 parts by weight of the lithium transition metal oxide contained in the mixture. Since the carbide (carbide) is mixed in an amount of 0.001 to 10 parts by weight relative to 100 parts by weight of lithium transition metal oxide, it can be uniformly distributed over the entire surface of the positive electrode active material particles, and the initial resistance and resistance increase rate can be reduced by securing excellent electrical conductivity. have.

On the other hand, the mixture may be prepared by adding and stirring the coating polymer in lithium transition metal oxide, and then adding and stirring the carbide, and at the same time, the coating polymer and carbide are added and stirred. It may be possible, and the order of the manufacturing process is not particularly limited. When the mixture is formed, a stirring process may be selectively performed, and in this case, the stirring speed may be 100 rpm and 2,000 rpm.

The mixture may include the coating polymer and carbide (carbide) in a weight ratio of 1:99 to 99:1, more preferably in a weight ratio of 20:80 to 80:20. By including the coating polymer and carbide within the weight ratio range, a coating layer in the form of a uniform film can be formed on the entire surface of the positive electrode active material particles, and carbide can be uniformly distributed. In addition, through this, it is possible to suppress side reactions with the electrolyte and the formation of a solid electrolyte interface (SEI) film on the surface of the positive electrode active material under high voltage, and to manufacture a positive electrode active material for high voltage resistance with improved resistance characteristics and life characteristics.

Next, the mixture is heat-treated to form a coating layer including a carbonized coating polymer and carbide on the surface of the particles of the lithium transition metal oxide.

The heat treatment for forming the coating layer may be performed in an oxidizing atmosphere such as air or oxygen or an inert atmosphere such as nitrogen, but more preferably, it may be performed in an oxidizing atmosphere.

The heat treatment may be performed at 200 to 800°C for 0.5 to 5 hours, more preferably at 300 to 600°C for 0.5 to 5 hours.

The positive electrode active material for a secondary battery of the present invention prepared as described above is lithium transition metal oxide; And a coating layer formed on the surface of the particles of the lithium transition metal oxide, wherein the coating layer is formed in a film form, and the coating layer includes a carbonized coating polymer and carbide.

The coating polymer used in the coating process can form a coating layer in a carbonized form through heat treatment during the coating process. Additional electrical conductivity may be secured due to the carbonized coating polymer.

The carbide (carbide) can remain without being decomposed into CO ₂ or CO even during high temperature heat treatment in an oxidizing atmosphere during the coating process, forming a coating layer with the coating polymer, and uniformly distributed on the surface of the positive electrode active material particles. have.

The coating layer may contain 0.001 to 10 parts by weight of the carbide, more preferably 0.002 to 2 parts by weight, based on 100 parts by weight of the lithium transition metal oxide particles. Even during the heat treatment during the coating process, carbide remains without decomposition and removal to satisfy the above content, and since carbide is included within the above range, excellent electrical conductivity is secured, and initial resistance and resistance increase rate are reduced, It can be suitably applied as a high voltage positive electrode active material.

The types of the coating polymer and carbide are applied in the same manner as described in the method of manufacturing the positive electrode active material for a secondary battery of the present invention.

The coating layer is formed in the form of a film surrounding the particle surface of the lithium transition metal oxide, and the thickness of the coating layer may be 5 to 2,000 nm, more preferably 10 to 500 nm. If the thickness of the coating layer is less than 5 nm, it may be difficult to form a uniform coating layer because the coating layer is too thin, and if it exceeds 2,000 nm, there may be a problem of capacity reduction due to lowering of ion conductivity.

The positive electrode active material for secondary batteries manufactured by coating as a hybrid coating material of a coating polymer and carbide according to the present invention suppresses side reactions with the electrolyte under high voltage, and forms a solid electrolyte interface (SEI) film on the surface of the positive electrode active material. Can be suppressed, and accordingly, resistance characteristics and life characteristics under high voltage can be remarkably improved.

According to still another embodiment of the present invention, a positive electrode for a secondary battery and a lithium secondary battery including the positive electrode active material are provided.

Specifically, the positive electrode is formed on the positive electrode current collector and the positive electrode current collector, and includes a positive electrode active material layer including the positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on aluminum or stainless steel surfaces , Surface treatment with nickel, titanium, silver, or the like can be used. In addition, the positive electrode current collector may generally have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

In addition, the positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material described above.

At this time, the conductive material is used to impart conductivity to the electrode, and in the battery configured, it can be used without particular limitation as long as it has electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; Metal powders or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers, such as polyphenylene derivatives, etc. can be used, and 1 type or a mixture of 2 or more types can be used. The conductive material may typically be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

In addition, the binder serves to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, and carboxymethyl cellulose (CMC) ), starch, hydroxypropyl cellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluorine rubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode active material. Specifically, a composition for forming a positive electrode active material layer including the positive electrode active material and, optionally, a binder and a conductive material may be coated on the positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent generally used in the art, dimethyl sulfoxide (dimethyl sulfoxide, DMSO), isopropyl alcohol, isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or Water and the like, and among these, one kind alone or a mixture of two or more kinds can be used. The amount of the solvent is sufficient to dissolve or disperse the positive electrode active material, the conductive material, and the binder in consideration of the coating thickness and production yield of the slurry, and to have a viscosity capable of exhibiting excellent thickness uniformity when applied for the production of the positive electrode afterwards. Do.

In another method, the positive electrode may be produced by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the film obtained by peeling from the support on the positive electrode current collector.

According to another embodiment of the present invention, an electrochemical device including the anode is provided. The electrochemical device may be specifically a battery or a capacitor, or more specifically, a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode facing the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. In addition, the lithium secondary battery may further include a battery container for housing the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or the surface of stainless steel Carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode current collector may generally have a thickness of 3 to 500 μm, and, like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to enhance the bonding strength of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The negative active material layer optionally includes a binder and a conductive material together with the negative active material. The negative electrode active material layer is, for example, coated on a negative electrode current collector with a negative electrode active material, and optionally a composition for forming a negative electrode comprising a binder and a conductive material, or dried or cast the negative electrode forming composition on a separate support, , It can also be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; Metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy; Metal oxides capable of doping and dedoping lithium, such as SiO _β (0 <β <2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Or a complex containing the metal compound and the carbonaceous material, such as a Si-C composite or a Sn-C composite, and the like, or any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Soft carbon and hard carbon are typical examples of low crystalline carbon, and amorphous or plate-like, scaly, spherical or fibrous natural graphite or artificial graphite, and kissy graphite are examples of high crystalline carbon. graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes).

In addition, the binder and the conductive material may be the same as described above for the positive electrode.

Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions, and can be used without particular limitation as long as it is used as a separator in a general lithium secondary battery. On the other hand, it is preferable that it has low resistance and excellent electrolyte-moisturizing ability. Specifically, porous polymer films such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer, etc. A laminate structure of two or more layers of may be used. In addition, a conventional porous non-woven fabric, for example, a high-melting point glass fiber, non-woven fabric made of polyethylene terephthalate fiber or the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single layer or multi-layer structure.

In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. It does not work.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent, methyl acetate (methyl acetate), ethyl acetate (ethyl acetate), γ-butyrolactone (γ-butyrolactone), ε-caprolactone (ε-caprolactone), such as ester-based solvents; Ether-based solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (propylene carbonate, PC) and other carbonate-based solvents; Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a C2 to C20 straight-chain, branched or cyclic hydrocarbon group, and may include a double bond aromatic ring or ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Alternatively, sulfolanes may be used. Of these, carbonate-based solvents are preferred, and cyclic carbonates (for example, ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and low-viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, the mixture of the cyclic carbonate and the chain carbonate in a volume ratio of about 1:1 to about 1:9 may be used to exhibit excellent electrolyte performance.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ and the like can be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can be effectively moved.

In addition to the components of the electrolyte, the electrolyte includes haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, and tree for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery. Ethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, or aluminum trichloride may also be included. At this time, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

Since the lithium secondary battery comprising the positive electrode active material according to the present invention as described above stably exhibits excellent discharge capacity, output characteristics and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful for electric vehicle fields such as hybrid electric vehicle (HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack includes a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Alternatively, it can be used as a power supply for any one or more medium-to-large devices in a power storage system.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

Example 1

LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ , polyvinylidene fluoride (PVDF), and B ₄ C as carbide were mixed in a weight ratio of 100:2:0.1, and heat-treated at 400° C. for about 3 hours in an oxygen atmosphere to obtain the LiNi _0.6 Co _0.2 Mn _0.2 O _{2 on} the particle surface A coating layer was formed.

Example 2

It was prepared in the same manner as in Example 1, except that it was prepared by mixing Al ₄ C ₃ in place of B ₄ C as a carbide.

Example 3

It was prepared in the same manner as in Example 1, except that it was prepared by mixing polyvinylpyrrolidone (PVP) instead of polyvinylidene fluoride (PVDF) as a coating polymer.

Example 4

LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ , polyvinylidene fluoride (PVDF), and B ₄ C as carbide were mixed in a weight ratio of 100:0.2:0.5, and heat-treated at 400°C for about 3 hours in an oxygen atmosphere to obtain the LiNi _0.6 Co _0.2 Mn _A coating layer was formed on the surface of _0.2 O ₂ particles.

Comparative Example 1

LiNi _0.6 Co _0.2 Mn _0.2 O ₂ without a coating layer was prepared.

Comparative Example 2

LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ and H ₃ BO ₃ were mixed in a weight ratio of 100:0.1, and heat-treated at 400° C. for about 3 hours in an oxygen atmosphere to obtain the LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ The surface of the particles was coated.

Comparative Example 3

LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ , polyvinylidene fluoride (PVDF), and carbon black were mixed in a weight ratio of 100:2:0.1, and heat-treated at 400°C for about 3 hours in an oxygen atmosphere to the particle surface of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ To form a coating layer.

In the case of the coating layer thus prepared, the thickness was formed in a very non-uniform shape, and carbon black was not detected in the coating layer. This is thought to be due to the decomposition and removal of carbon black into CO ₂ or CO during the heat treatment process.

Comparative Example 4

LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ and B ₄ C were mixed at a weight ratio of 100:0.1, and heat-treated at 400° C. for about 3 hours in an oxygen atmosphere to coat the particle surfaces of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ .

Comparative Example 5

LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 100:2, and heat-treated at 400° C. for about 3 hours in an oxygen atmosphere to obtain the LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ The surface of the particles was coated.

[Experimental Example 1: Observation of positive electrode active material]

Figures 1 and 2 (Example 1) and 3, 4 (Comparative Example 2) show photographs of the positive electrode active material prepared according to Example 1 and Comparative Example 2 enlarged and observed with a scanning electron microscope (SEM). Done.

1 and 2, Example 1 prepared by coating as a hybrid coating material of a coating polymer and carbide is that the coating layer in the form of a film surrounding the surface of the active material particles is formed to have an average thickness of 1,000 nm. I could confirm.

Referring to FIGS. 3 and 4, it can be seen that in Comparative Example 2 coated with an existing coating material, H ₃ BO ₃ , a coating portion in the form of an island rather than a film form was formed on the surface of the active material particle.

[Experimental Example 2: Evaluation of high voltage cycle characteristics]

A composition for forming a positive electrode by using the positive electrode active material prepared in Examples 1 to 4 and Comparative Examples 1 to 5, and mixing carbon black and PVDF binder in an N-methylpyrrolidone solvent in a weight ratio of 96:2:2 Was prepared, coated on one side of an aluminum current collector, dried at 130° C., and then rolled to prepare a positive electrode, respectively.

In addition, natural graphite, carbon black conductive material, and PVdF binder as negative electrode active materials were mixed in an N-methylpyrrolidone solvent in a weight ratio of 85:10:5 to prepare a composition for forming a negative electrode, and this was prepared on one side of a copper current collector. Coated on to prepare a negative electrode.

An electrode assembly was manufactured by interposing a separator of porous polyethylene between the positive electrode and the negative electrode prepared as described above, and after placing the electrode assembly inside the case, an electrolyte was injected into the case to prepare a lithium secondary battery. At this time, the electrolyte was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF ₆ ) in an organic solvent consisting of ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate (EC/DMC/EMC mixing volume ratio = 3/4/3). I did.

Each lithium secondary battery cell (full cell) prepared as described above was charged at 25°C and 45°C in CCCV mode until 0.7C and 4.4V, respectively, and cut off at 0.55C condition, and a constant current of 0.5C By discharging it to 3.0V, charging and discharging was performed 100 times to measure the capacity retention rate (Capacity Retention [%]). The results are shown in Table 1.

Capacity retention rate (%) after 100 cycles 25℃ 45℃ Example 1 98.6 95.7 Example 2 95.3 93.0 Example 3 97.7 94.8 Example 4 98.1 95.6 Comparative Example 1 90.4 88.1 Comparative Example 2 91.4 90.5 Comparative Example 3 91.0 88.4 Comparative Example 4 91.2 90.6 Comparative Example 5 92.7 90.8

Referring to Table 1, Examples 1 to 4 prepared by coating as a hybrid coating material of a coating polymer and carbide are Comparative Example 1 without coating or a comparison coated with H ₃ BO ₃ as an existing coating material. Compared to Example 2, the cycle torque at room temperature (25°C) and high temperature (45°C) under high voltage was remarkably excellent. In addition, the cycle characteristics of Examples 1 to 4 were remarkably excellent even compared with Comparative Example 3 in which polymer and carbon (carbon black) were coated as a coating material. In addition, in the case of Comparative Example 4 in which B ₄ C was coated as a single coating material, the cycle resistance at room temperature (25° C.) and high temperature (45° C.) was lower than that of Examples 1 to 4, and showed a similar level to that of Comparative Example 2. . In addition, in the case of Comparative Example 5 coated with PVDF as a single coating material, the cycle characteristics at room temperature (25°C) and high temperature (45°C) were significantly lower than in Examples 1 to 4.

[Experimental Example 3: Evaluation of high voltage cell resistance characteristics]

Each lithium secondary battery cell (full cell) prepared as described above was charged at 25°C and 45°C in CCCV mode until 0.7C and 4.4V, respectively, and cut off at 0.55C condition, and a constant current of 0.5C The resistance increase rate (DCIR[%]) was measured while discharged to 3.0V and charged and discharged 100 times. The results are shown in Table 2.

Resistance increase rate (%) after 100 cycles 25℃ 45℃ Example 1 14 25 Example 2 13 27 Example 3 18 30 Example 4 17 22 Comparative Example 1 32 51 Comparative Example 2 29 48 Comparative Example 3 31 49 Comparative Example 4 25 43 Comparative Example 5 35 52

Referring to Table 2, Examples 1 to 4 prepared by coating as a hybrid coating material of a coating polymer and carbide are Comparative Example 1 without coating or a comparison coated with H ₃ BO _{3 which} is an existing coating material. Compared to Example 2, the rate of increase in resistance at room temperature and high temperature (45° C.) under high voltage was significantly reduced. In addition, the resistance properties of Examples 1 to 4 were remarkably excellent even when compared to Comparative Example 3 in which polymer and carbon (carbon black) were coated as a coating material. In addition, in the case of B ₄ C alone coating performed in Comparative Example 4, Example It showed a higher resistance increase rate compared to 1 to 4. This is considered to be because in the case of Examples 1 to 4, the resistance increase rate was reduced due to the improvement of the surface electrical conductivity and suppression of the generation of side-reactants by the uniform coating of polymer-carbide, and as in Comparative Example 4, a single coating of conductive carbide It is believed that this is because a uniform coating is not formed on the surface of the positive electrode active material.

In addition, in the case of the PVDF alone coating of Comparative Example 5, a relatively high resistance increase rate was exhibited, which increased the initial resistance of the polymer itself and the resistance increase rate during charging and discharging continuously.

Claims (17)

Preparing a lithium transition metal oxide;
Forming a mixture by mixing the lithium transition metal oxide, a coating polymer, and a carbide; And
Heat-treating the mixture to form a coating layer including a carbonized coating polymer and carbide on the surface of the particles of the lithium transition metal oxide; and
The lithium transition metal oxide is lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium iron phosphate compound (LiFePO ₄ ), and a lithium composite transition represented by Formula 1 below. Method for producing a cathode active material for a secondary battery comprising at least one or more selected from the group consisting of metal oxides:
[Formula 1]
Li _p Ni _1-xy Co _x M ^a _y M ^b _z O ₂
In the above formula, M ^a is at least one element selected from the group consisting of Mn, Al and Zr, and M ^b is at least one selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo, W and Cr The above elements are 0.9≦p≦1.5, 0≦x≦0.5, 0≦y≦0.5, and 0≦z≦0.1.
The method of claim 1,
The coating polymer is polyvinylidene fluoride (PVDF), polyvinylpyrrolidone, polyethylene, polystyrene, polyethylene terephthalate, polyvinyl chloride, polyvinylidene chloride, epoxy resin, amino resin, phenol resin, poly Method for producing a positive electrode active material for a secondary battery at least one selected from the group consisting of ester resins.
The method of claim 1,
The carbide (carbide) is at least one selected from the group consisting of B ₄ C, Al ₄ C ₃ , TiC, TaC, WC, NbC, HfC, VC, and ZrC. Method for producing a cathode active material for a secondary battery.
The method of claim 1,
The mixture is a method for producing a positive electrode active material for a secondary battery comprising 0.001 to 10 parts by weight of the coating polymer based on 100 parts by weight of lithium transition metal oxide.
The method of claim 1,
The mixture comprises 0.001 to 10 parts by weight of the carbide based on 100 parts by weight of the lithium transition metal oxide method for producing a cathode active material for a secondary battery.
The method of claim 1,
The mixture is a method for producing a positive electrode active material for a secondary battery comprising the coating polymer and carbide (carbide) in a weight ratio of 1:99 to 99:1.
delete The method of claim 1,
The heat treatment is a method of manufacturing a positive electrode active material for a secondary battery performed at 200 to 800 ℃.
Lithium transition metal oxide; And
Includes; a coating layer formed on the particle surface of the lithium transition metal oxide,
The coating layer is made in the form of a film,
The coating layer includes a carbonized coating polymer and carbide,
The lithium transition metal oxide is lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium iron phosphate compound (LiFePO ₄ ), and a lithium composite transition represented by Formula 1 below. A cathode active material for secondary batteries comprising at least one or more selected from the group consisting of metal oxides:
[Formula 1]
Li _p Ni _1-xy Co _x M ^a _y M ^b _z O ₂
In the above formula, M ^a is at least one element selected from the group consisting of Mn, Al and Zr, and M ^b is at least one selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo, W and Cr The above elements are 0.9≦p≦1.5, 0≦x≦0.5, 0≦y≦0.5, and 0≦z≦0.1.
The method of claim 9,
The coating polymer is polyvinylidene fluoride (PVDF), polyvinylpyrrolidone, polyethylene, polystyrene, polyethylene terephthalate, polyvinyl chloride, polyvinylidene chloride, epoxy resin, amino resin, phenol resin, poly At least one positive electrode active material for secondary batteries selected from the group consisting of ester resins.
The method of claim 9,
The coating polymer is at least one selected from the group consisting of polyvinylidene fluoride (PVDF) and polyvinylpyrrolidone, polyethylene terephthalate, and polyvinylidene chloride.A cathode active material for a secondary battery.
The method of claim 9,
The carbide (carbide) is at least one selected from the group consisting of B ₄ C, Al ₄ C ₃ , TiC, TaC, WC, NbC, HfC, VC, and ZrC.
The method of claim 9,
The carbide (carbide) is B ₄ C or Al ₄ C _{3 A} cathode active material for a secondary battery.
The method of claim 9,
The coating layer is a positive electrode active material for secondary batteries having a thickness of 5 to 2,000 nm.
The method of claim 9,
The coating layer is a cathode active material for a secondary battery containing 0.001 to 10 parts by weight of the carbide (carbide) based on 100 parts by weight of lithium transition metal oxide particles.
A positive electrode for a secondary battery comprising the positive electrode active material according to any one of claims 9 to 15.
A lithium secondary battery comprising the positive electrode according to claim 16.

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